The present invention relates to a method and apparatus for determining and regulating the characteristics (especially the density) of continuous rod-like fillers consisting of tobacco filaments of a tobacco smoke filtering material or other fibrous substances. More particularly, the invention relates to improvements in a method and apparatus for monitoring the characteristics of a continuous rod-like filler of fibrous material with the aid of a detector including a source of beta rays.
It is known to employ beta ray detectors as a means for determining the density of a continuous rod-like filler consisting of tobacco or filter material. A beta ray detector comprises a radiation source which is located at one side of the path for a continuously moving (wrapped or unwrapped) filler and an ionization chamber or another suitable transducer which is located at the other side of the path opposite the radiation source. The rays which reach the transducer are weakened during passage through the filler so that their intensity indicates the density of the filler and the transducer furnishes a continuous signal whose intensity fluctuates as a function of variations in the density of the filler. Such detectors are often employed in cigarette rod making and analogous machines wherein a continuous rod including a rod-like tobacco filler or a filler consisting of fibrous filter material and a tubular wrapper of cigarette paper or the like is moved lengthwise past a cutoff which subdivides the rod into plain cigarettes, cigarillos, cigars or filter rod sections of unit length or multiple unit length.
It is also known to compensate for those fluctuations in the intensity of beta rays which are attributable to stochastic (randomly occurring) disintegration of nuclei of radioactive material. Such fluctuations are filtered out by resorting to low-pass filters (e.g., R C stages) in order to insure that signals which are used to regulate the operation of the rod-making machine indicate only the density of measured portions of the rod and are not distorted by other phenomena, such as disintegration of nuclei in the source of radioactive radiation. A drawback of presently employed low-pass filters is that their inertia (time constant) is relatively high so that the interval of time which elapses between a measurement and the generation of a signal which indicates the average density of the measured portion of the rod is rather long. Attempts to reduce the length of such intervals include the utilization of high-intensity beta radiation sources (usually strontium 90). This, however, can present a serious danger to the attendants and neccessitates stringent and expensive safety measures. Therefore, manufacturers of smoker's products do not favor the utilization of such density monitoring devices.
If the intensity of beta radiation is reduced to a relatively low value, the delay in generating signals which represent the average density of a rod-like filler of tobacco or filter material is so great that the apparatus employing such monitoring devices cannot be used to determine the average density of relatively short sections of fillers, e.g., sections whose length at most equals that of a plain cigarette or filter plug of unit length. On the other hand, it is often desirable to regulate the density of fillers in cigarettes or other rod-shaped smoker's products in such a way that the density of each and every cigarette or the density of selected portions of discrete cigarettes (e.g.,. of cigarette ends) matches a predetermined value. A prerequisite for such accurate regulation of density is a reliable measurement and immediate indication of density in extremely short portions of a continuously moving rod-like filler.